Device for non-dissipative measurement of the current in an inductor

Abstract

The invention relates to a device for measuring current in an inductor, which device is intended to be connected in parallel with said inductor, comprising two terminals A and B. The device comprises: a network in parallel with the inductor and connected to the terminals A and B having a resistor R2 in series with a resistor R1 in parallel with a capacitor C1; a voltage offset circuit having a DC voltage generator E connected in parallel with an offset resistor (Roffset) in series with two resistors in parallel R3 and R4, the positive pole of this voltage source being connected to terminal B of the inductor; a temperature compensation circuit comprising a current source controlled as a function of the temperature, one of the two terminals of the current source being connected to the negative pole of the generator E, the other terminal of the current source being connected to different points of the measurement device according to the direction of variation of the current of the source as a function of the temperature. The measurement of voltage Vmes, the image of the current I in the inductor 12, is performed between the common point between the resistors R1, R2 of the network and the common point between the offset resistor and the two resistors R3 and R4.

Description

FIELD OF THE INVENTION [0001] The invention relates to an inexpensive and compact non-dissipative measurement device for the current flowing through an inductor inserted into an electrical or electronic device. BACKGROUND OF THE INVENTION [0002] In certain electronic applications it is necessary to measure the value of the current in the inductors with good accuracy and while disturbing as little as possible the device in which the inductor is inserted. We may cite for example the measurement of the current in the inductors of switched mode power supplies, among other things, voltage step-down or step-up switched mode serial choppers (respectively known as “buck converters” and “boost converters”). [0003] The conventional method which is most used consists in placing a measurement shunt in series with the inductor, thereby making it possible to obtain the image of the current in the inductor by measuring the voltage across the terminals of the shunt. This solution has the advantage ...

AI Technical Summary

Benefits of technology

[0037] This device makes it possible, by injection of current controlled as a function of temperature, to obtain a voltage (Vmes) which is the image of the current in the inductor regardless of the temperature of the latter.

[0042] A capacitor C1′ may be added in parallel with R3 and R4 so as to improve the operation of the device and increase its precision.

Problems solved by technology

This solution has the advantage of being simple to implement, on the other hand it has a major drawback.

Specifically, the power dissipated in the shunt contributes to a degradation in the overall efficiency of the converter, which is not always acceptable, this being all the more true when the output voltage of the energy conversion device is low.

However the device of the prior art represented in FIG. 2, has a major drawback since the value of the resistance RL of the inductor depends on the temperature to which it is subjected, the current measurement which is obtained therefore exhibits an error related to the temperature.

The consequence is that the measurement of the current in the inductor and therefore the limitation of current Ilim depends on the temperature.

The variation in the limitation current as a function of the temperature is 60% between −40° C and 100° C. Such a scatter in the value of the limiting current gives rise to an oversizing of the power circuit so that it can withstand the limiting current at low temperature, this representing a major drawback.

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